There are many commercial and industrial protective and/or decorative coatings for use on walls, machines, and other such entities requiring protective coatings. Polyurethane coatings are known in the industry as one of the toughest coatings available. However, due to certain problems, there is a reluctance to use such coatings.
The industry, for the most part, resorts to a two package system to overcome the problems of combining color pigments and isocyanate polymers to create a moisture curing polyurethane. One of such problems is that the color pigments contain absorbed moisture on their surfaces that cause the polyurethane formula to gel within a few days, becoming hard and unfit for commercial use.
There are many polyisocyanates that react with atmospheric water at room temperatures and form useful films that are used in a limited form as moisture curing polyurethane coatings. This type of coating is one of the finest coatings available that can be produced without the use of heat or other external sources of energy being applied. They are very useful for objects that cannot be heated such as prefabricated metal building, plastics, large machinery, air planes, ships, etc.
In preparing a polyurethane coating using the two package method, a polyol is chosen that will chemically combine with a suitable polyisocyanate. The polyol portion is pigmented to achieve the desired color, opacity, etc. The pigmented polyol portion and the polyisocyanate are supplied in separate containers to the ultimate user or consumer. The consumer mixes the two portions in accordance with the ratio specified by the manufacturer just prior to use. This admixture hs a limited life and must be used up within a relatively short period of time or it will harden and become unusable. This approach is not only cumbersome but expensive in that it results in a quantity of hardened and wasted material if the entire admixture is not used up. There is also a risk in that the pigmented polyol portion and the polyisocyanate portion will not be mixed in the correct ratio causing serious damage to the performance of the resulting polyurethane coating. In addition, atmospheric moisture is a significant factor in using the two package method in that water also cures isocyanates. On a hot, humid day, a large portion of the polyisocyanate is cured by atmospheric moisture leaving a portion of the polyol with nothing to cross link itself with, resulting in a coating less desirable than if the polyol was completely cross linked. Likewise, on a cold, dry day more of the polyol will cross link with the polyisocyanates. It is apparent that the two package polyurethane coating method will produce a quality of coating dependent upon atmospheric conditions said conditions being almost always impossible to control, and if so, very expensive.
Moisture curing polyurethane coatings can be made in a single package method eliminating all the above mentioned problems of the two package types. However, the current methods for making such a single package system is cumbersome and expensive to the consumer. The existing methods for preparing color pigmented polyurethane coatings in a single package requires expensive equipment to dry the color pigments; or, they require the sacrifice of some of the critical properties of the final coating film, such as loss of gloss, high risk of toxicity during application, lack of film strength, etc. Disadvantages of preparing moisture curing color pigmented polyurethane coatings are: use of Molecular Sieves which cause the coatings to lose their gloss and to sometimes gel due to the alkalinity of some of the Molecular Sieves; the use of mono functional isocyanates which is expensive and also hazardous due to their highly volatile nature; the use of Ethyl Ortho Formate to dehydrate the pigments results in the formulation of alcohols which degrade the final coating film; the use of diisocyanates requires an excess which can generate a toxicity problem.
The majority of the moisture curing polyurethanes manufacturers, for the above reasons, manufacture moisture curing polyurethanes in a clear form or pigmented with metallic pigments like aluminum. Metallic pigments contain little or no moisture and hence the moisture problems inherent in color pigments do not exist; the color pigments have enough absorbed moisture in them to render them unfit for use in moisture curing polyurethane coatings.
There is a need for a process of easily, efficiently and inexpensively manufacturing pigmented moisture curing polyurethane coatings on a commercial basis. I am not aware of any means or methods for commercially producing a stable moisture curing polyurethane coating that can be offered for sale in a single package that is efficient and inexpensive, in comparison to existing methods.